To fix that with strobing while avoiding adding on too much VSYNC ON lag -- it is preferable to have "frame rate = refresh rate = strobe rate" -- and for slightly lower input lag with Fast Sync without adding strobed jitteriness -- try a frame rate cap of double the refresh rate when using Fast Sync (or the new graphics-card-independent RTSS Scanline Sync feature, to simulate NVIDIA Fast Sync or AMD Enhanced Sync)